252 SpA Mega Latios Hidden Power Fire vs. 0 HP / 0 SpD Bisharp: 204-242 (75.2 - 89.2%) -- guaranteed 2HKOI personally support keeping M-Latios ranked, but you neglect to mention in your post that if you happen to build a Latios team without a mega there is literally no reason to not use Mega Latios unless you are running Dual Screens as, if you look at the two in a vaccum (i.e. looking at the pokemon themselves without worrying about the presence of other megas), Mega Latios is better than LO Latios due to the fact that the small decrease in special power (this is very rarely noticeable anyway tbh) is completely outweighed by the lack of LO recoil, the "resistance" to Knock Off, the noticable increase in bulk and (if applicable) lacking need of investment for EQ due to the naturally higher power than LO Latios' EQ. The points as to why it is so low are correct in your post tho :)
252 SpA Life Orb Latios Hidden Power Fire vs. 0 HP / 0 SpD Bisharp: 229-270 (84.5 - 99.6%) -- guaranteed 2HKO
252 SpA Mega Latios Surf vs. 0 HP / 0 SpD Heatran: 218-258 (67.4 - 79.8%) -- guaranteed 2HKO
252 SpA Life Orb Latios Surf vs. 0 HP / 0 SpD Heatran: 244-289 (75.5 - 89.4%) -- guaranteed 2HKO
Idk, that is a pretty large difference in power.
Considering that there are a wide array of Megas to choose from and how much a team benefits from having many of the top Mega threats in the OU metagame, the amount of teams that do not require any other Mega Pokemon is limited to a very, very small fraction of teams. More power on Earthquake is indeed nice to have, but almost all teams can find a Mega Pokemon that they can benefit from before they resort to Mega Latios.